U.S. patent number 11,187,287 [Application Number 17/011,035] was granted by the patent office on 2021-11-30 for method for controlling engagement of engine clutch of hybrid electric vehicle.
This patent grant is currently assigned to HYUNDAI MOTOR COMPANY, KIA MOTORS CORPORATION. The grantee listed for this patent is Hyundai Motor Company, KIA Motors Corporation. Invention is credited to Kwon Chae Chung, Chun Hyuk Lee, Seong Ik Park.
United States Patent |
11,187,287 |
Lee , et al. |
November 30, 2021 |
Method for controlling engagement of engine clutch of hybrid
electric vehicle
Abstract
Disclosed is a method for controlling engagement of an engine
clutch in a hybrid electric vehicle in which an engagement control
method of the engine clutch is accurately determined so as to
minimize a determination error and a sense of discontinuity caused
by conversion of the engagement control method resulting
therefrom.
Inventors: |
Lee; Chun Hyuk (Hwaseong-si,
KR), Chung; Kwon Chae (Seoul, KR), Park;
Seong Ik (Seoul, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Hyundai Motor Company
KIA Motors Corporation |
Seoul
Seoul |
N/A
N/A |
KR
KR |
|
|
Assignee: |
HYUNDAI MOTOR COMPANY (Seoul,
KR)
KIA MOTORS CORPORATION (Seoul, KR)
|
Family
ID: |
1000005966105 |
Appl.
No.: |
17/011,035 |
Filed: |
September 3, 2020 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20210164528 A1 |
Jun 3, 2021 |
|
Foreign Application Priority Data
|
|
|
|
|
Dec 2, 2019 [KR] |
|
|
10-2019-0158005 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60K
6/387 (20130101); F16D 48/08 (20130101); F16D
2500/3108 (20130101); F16D 2500/10412 (20130101); B60Y
2300/18025 (20130101); F16D 2500/30806 (20130101); F16D
2500/3127 (20130101); F16D 2500/3109 (20130101); F16D
2500/3067 (20130101); F16D 2500/3107 (20130101); F16D
2500/3121 (20130101); F16D 2500/30406 (20130101); F16D
2500/3065 (20130101); B60Y 2200/92 (20130101) |
Current International
Class: |
F16D
48/08 (20060101); B60K 6/387 (20071001) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hlavka; David J
Attorney, Agent or Firm: McDonnell Boehnen Hulbert &
Berghoff LLP
Claims
What is claimed is:
1. A method for controlling engagement of an engine clutch in a
hybrid electric vehicle, the method comprising: determining whether
or not driving of the hybrid electric vehicle using power of a
motor and power of an engine is required during driving using the
power of the motor alone; determining whether or not at least one
of two or more conditions for execution of a synchronization
engagement control of the engine clutch is satisfied, when driving
of the hybrid electric vehicle using the power of the motor and the
power of the engine is required; executing the synchronization
engagement control, when the at least one of the two or more
conditions for execution of the synchronization engagement control
is satisfied; and executing a launch slip engagement control of the
engine clutch, when all of the two or more conditions for execution
of the synchronization engagement control are not satisfied.
2. The method of claim 1, wherein a first condition for execution
of the synchronization engagement control is that a real-time
revolutions per minute (RPM) of the motor is a first RPM or more,
and the first RPM is set to a motor RPM value at which the motor
may transmit power to wheels by tracking a torque of the engine
when the engine clutch is directly connected.
3. The method of claim 1, wherein a second condition for execution
of the synchronization engagement control is that a maximum RPM of
the motor which may maintain a maximum torque of the motor based on
a real-time available power of the motor is an engine clutch direct
connection RPM or more, and the engine clutch direct connection RPM
is an RPM at a point in time when the power of the engine starts to
be transmitted to a drive shaft of the hybrid electric vehicle by
direct connection of the engine clutch.
4. The method of claim 1, wherein a third condition for execution
of the synchronization engagement control is that a maximum RPM of
the motor which may satisfy a driver request torque based on a
real-time available power of the motor is an engine clutch direct
connection RPM or more, and the engine clutch direct connection RPM
is an RPM at a point in time when the power of the engine starts to
be transmitted to a drive shaft of the hybrid electric vehicle by
direct connection of the engine clutch.
5. The method of claim 1, wherein a fourth condition for execution
of the synchronization engagement control is that acceleration
linearity of the hybrid electric vehicle is satisfied, and when an
excess acceleration of the hybrid electric vehicle is a threshold
acceleration or more, it is determined that the acceleration
linearity of the hybrid electric vehicle is satisfied.
6. The method of claim 5, wherein the excess acceleration is
calculated as a value acquired by dividing an excess torque of the
hybrid electric vehicle by a weight of the hybrid electric vehicle,
the excess torque is calculated as a value acquired by subtracting
a driving load of the hybrid electric vehicle from an available
torque of the hybrid electric vehicle, and the available torque of
the hybrid electric vehicle is calculated as a value acquired by
dividing a motor torque by a gear ratio of a transmission and a
dynamic radius of tires.
7. The method of claim 6, wherein the driving load of the hybrid
electric vehicle is calculated by an equation "Driving
Load=(.mu..times.m.times.g.times.sin .theta.)+(Drag Torque of
Transmission.times.V)+(1/2.times..rho..times.Cd.times.A.times.V.sup.2)",
wherein .mu. is a rolling resistance of the tires, m is the weight
of the hybrid electric vehicle, g is acceleration due to gravity,
.theta. is a slope of a driving road, V is a vehicle speed, .rho.
is air density, Cd is an air resistance coefficient of the hybrid
electric vehicle, and A is a cross-sectional area of the hybrid
electric vehicle which encounters air resistance during
driving.
8. The method of claim 5, wherein the threshold acceleration is an
acceleration value set according to a gear ratio of a transmission
configured to connect the motor and a drive shaft.
9. The method of claim 1, wherein, when a reference time elapses
before direct connection of the engine clutch during the execution
of the synchronization engagement control, the execution of the
synchronization engagement control is stopped and the launch slip
engagement control starts to be executed.
10. The method of claim 9, wherein the reference time is determined
depending on an SOC of a battery used as a power of the motor, a
slope of a driving road, and a gear ratio of a transmission.
11. The method of claim 1, wherein the synchronization engagement
control is an engagement control method in which the engine clutch
is directly connected after RPMs of the engine and the motor are
synchronized.
12. The method of claim 1, wherein the launch slip engagement
control is an engagement control method in which slip control of
the engine clutch is performed before RPMs of the engine and the
motor are synchronized, and when the RPM of the motor is
synchronized with the RPM of the engine, the engine clutch is
directly connected.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims under 35 U.S.C. .sctn. 119(a) the benefit
of priority to Korean Patent Application No. 10-2019-0158005 filed
on Dec. 2, 2019, the entire contents of which are incorporated
herein by reference.
FIELD
The present disclosure relates to a method for controlling
engagement of an engine clutch in a hybrid electric vehicle. More
particularly, it relates to a method for controlling engagement of
an engine clutch in a hybrid electric vehicle in which an
engagement control method of the engine clutch is accurately
determined so as to minimize a determination error and a sense of
discontinuity caused by conversion of the engagement control method
resulting therefrom.
BACKGROUND
In general, a hybrid electric vehicle uses a combination of power
of an engine and power of a motor during driving of the vehicle,
and an engine clutch is installed between the engine and the motor.
The engine clutch may transmit power between the engine and the
motor.
The conventional hybrid vehicle drives using only power of the
motor upon initial launching of the vehicle during parking, and
then uses power of the engine according to a driver request or the
state of charge (SOC) of a battery. The power of the engine may be
transmitted to wheels through the engine clutch and a transmission,
and excess power out of the power of the engine may charge the
battery using the motor.
In order to transmit the power of the engine to the wheels or to
use the power of the engine to charge the battery, the engine
clutch should be engaged.
The maneuvers to control engagement of the engine clutch may be
classified into two methods, i.e., synchronization engagement
control and launch slip engagement control. In the synchronization
engagement control, RPMs of the engine and the motor are
synchronized and then the engine clutch is directly connected. In
the launch slip engagement control, slip control of the engine
clutch is performed before the RPMs of the engine and the motor are
synchronized, and when the RPM of the motor is synchronized with
the RPM of the engine, the engine clutch is directly connected.
Conventionally, when the engagement control method of the engine
clutch at an initial stage of launching of a vehicle is initially
determined, the synchronization engagement control is
preferentially attempted. Thereafter, time-out conditions depending
on a vehicle state and driving conditions are applied, and thus,
when a designated time corresponding to the time-out conditions
elapses during execution of the synchronization engagement control,
the launch slip engagement control starts to be executed. The
reason for this is that a control factor to determine the engine
clutch engagement control method is not clear, and conversion of
the engine clutch engagement control method to the launch slip
engagement control during execution of the synchronization
engagement control is possible but conversion of the engine clutch
engagement control method to the synchronization engagement control
during execution of the launch slip engagement control is not
possible.
The reason why conversion of the engine clutch engagement control
method to the launch slip engagement control during execution of
the synchronization engagement control is allowable but conversion
of the engine clutch engagement control method to the
synchronization engagement control during execution of the launch
slip engagement control is not possible is that, if an engine
torque is used to control the speed of the engine while the engine
torque is transmitted to wheels through slip control of the engine
clutch, a drivability problem occurs.
SUMMARY OF THE DISCLOSURE
The present disclosure has been made in an effort to solve the
above-described problems associated with the prior art, and it is
an object of the present disclosure to provide a method for
controlling engagement of an engine clutch in a hybrid electric
vehicle in which an engagement control method of the engine clutch
is accurately determined so as to minimize a determination error
and a sense of discontinuity caused by conversion of the engagement
control method resulting therefrom.
In one aspect, the present disclosure provides a method for
controlling engagement of an engine clutch in a hybrid electric
vehicle, the method including determining whether or not driving of
the vehicle using power of a motor and power of an engine is
required during driving using the power of the motor alone,
determining whether or not at least one of two or more conditions
for execution of synchronization engagement control of the engine
clutch is satisfied, when driving of the vehicle using the power of
the motor and the power of the engine is required, executing the
synchronization engagement control, when the at least one of the
two or more conditions for execution of the synchronization
engagement control is satisfied, and executing launch slip
engagement control of the engine clutch, when all of the two or
more conditions for execution of the synchronization engagement
control are not satisfied.
In a preferred embodiment, a first condition for execution of the
synchronization engagement control may be that a real-time
revolutions per minute (RPM) of the motor is a first RPM or more,
and the first RPM may be set to a motor RPM value at which the
motor may transmit power to wheels by tracking a torque of the
engine when the engine clutch is directly connected. In another
preferred embodiment, a second condition for execution of the
synchronization engagement control may be that a maximum RPM of the
motor which may maintain a maximum torque of the motor based on a
real-time available power of the motor is an engine clutch direct
connection RPM or more, and the engine clutch direct connection RPM
may be an RPM at a point in time when the power of the engine
starts to be transmitted to a drive shaft of the vehicle by direct
connection of the engine clutch. In still another preferred
embodiment, a third condition for execution of the synchronization
engagement control may be that a maximum RPM of the motor which may
satisfy a driver request torque based on a real-time available
power of the motor is an engine clutch direct connection RPM or
more, and the engine clutch direct connection RPM may be an RPM at
a point in time when the power of the engine starts to be
transmitted to a drive shaft of the vehicle by direct connection of
the engine clutch.
In yet another preferred embodiment, a fourth condition for
execution of the synchronization engagement control may be that
acceleration linearity of the vehicle is satisfied, and when an
excess acceleration of the vehicle is a threshold acceleration or
more, it may be determined that the acceleration linearity of the
vehicle is satisfied. In still yet another preferred embodiment,
the excess acceleration may be calculated as a value acquired by
dividing an excess torque of the vehicle by a weight of the
vehicle, the excess torque may be calculated as a value acquired by
subtracting a driving load of the vehicle from an available torque
of the vehicle, and the available torque of the vehicle may be
calculated as a value acquired by dividing a motor torque by a gear
ratio of a transmission and a dynamic radius of tires.
In a further preferred embodiment, the driving load of the vehicle
may be calculated by an equation "Driving
Load=(.mu..times.m.times.g.times.sin .theta.)+(Drag Torque of
Transmission.times.V)+(1/2.times..rho..times.Cd.times.A.times.V.sup.2)",
.mu. may be a rolling resistance of the tires, m may be the weight
of the vehicle, g may be acceleration due to gravity, .theta. may
be a slope of a driving road, V may be a vehicle speed, .rho. may
be air density, Cd may be an air resistance coefficient of the
vehicle, and A may be a cross-sectional area of the vehicle which
encounters air resistance during driving. In another further
preferred embodiment, the threshold acceleration may be an
acceleration value set according to a gear ratio of a transmission
configured to connect the motor and a drive shaft.
In still another further preferred embodiment, when a reference
time elapses before direct connection of the engine clutch during
the execution of the synchronization engagement control, the
execution of the synchronization engagement control may be stopped
and the launch slip engagement control may start to be executed. In
yet another further preferred embodiment, the reference time may be
determined depending on an SOC of a battery used as a power of the
motor, a slope of a driving road, and a gear ratio of a
transmission.
Other aspects and preferred embodiments of the disclosure are
discussed infra.
The above and other features of the disclosure are discussed
infra.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features of the present disclosure will now be
described in detail with reference to certain exemplary embodiments
thereof illustrated in the accompanying drawings which are given
hereinbelow by way of illustration only, and thus are not
limitative of the present disclosure, and wherein:
FIG. 1 is a view schematically illustrating a TMED system of a
hybrid electric vehicle;
FIG. 2A is a graph comparatively illustrating changes in RPMs and
torques in synchronization engagement control and launch slip
engagement control of an engine clutch;
FIG. 2B is another graph comparatively illustrating changes in RPMs
and torques in synchronization engagement control and launch slip
engagement control of an engine clutch;
FIG. 2C is another graph comparatively illustrating changes in RPMs
and torques in synchronization engagement control and launch slip
engagement control of an engine clutch;
FIG. 2D is another graph comparatively illustrating changes in RPMs
and torques in synchronization engagement control and launch slip
engagement control of an engine clutch;
FIG. 2E is another graph comparatively illustrating changes in RPMs
and torques in synchronization engagement control and launch slip
engagement control of an engine clutch;
FIG. 2F is another graph comparatively illustrating changes in RPMs
and torques in synchronization engagement control and launch slip
engagement control of an engine clutch;
FIG. 3 is a flowchart representing a method for controlling
engagement of an engine clutch in accordance with the present
disclosure;
FIG. 4A is a graph for explaining a first condition in accordance
with the present disclosure;
FIG. 4B is another graph for explaining a first condition in
accordance with the present disclosure;
FIG. 5 is a graph for explaining a second condition in accordance
with the present disclosure;
FIG. 6 is a graph for explaining a third condition in accordance
with the present disclosure;
FIG. 7 is a graph for explaining a fourth condition in accordance
with the present disclosure;
FIG. 8A is a graph representing conversion of an engagement control
method to launch slip engagement control during execution of
synchronization engagement control;
FIG. 8B is another graph representing conversion of an engagement
control method to launch slip engagement control during execution
of synchronization engagement control; and
FIG. 8C is another graph representing conversion of an engagement
control method to launch slip engagement control during execution
of synchronization engagement control.
It should be understood that the appended drawings are not
necessarily to scale, presenting a somewhat simplified
representation of various preferred features illustrative of the
basic principles of the disclosure. The specific design features of
the present disclosure as disclosed herein, including, for example,
specific dimensions, orientations, locations, and shapes will be
determined in part by the particular intended application and use
environment.
In the figures, reference numbers refer to the same or equivalent
parts of the present disclosure throughout the several figures of
the drawings.
DETAILED DESCRIPTION
Hereinafter reference will now be made in detail to various
embodiments of the present disclosure, examples of which are
illustrated in the accompanying drawings and described below. While
the disclosure will be described in conjunction with exemplary
embodiments, it will be understood that present description is not
intended to limit the disclosure to those exemplary embodiments. On
the contrary, the disclosure is intended to cover not only the
exemplary embodiments, but also various alternatives,
modifications, equivalents and other embodiments, which may be
included within the spirit and scope of the disclosure as defined
by the appended claims.
Referring to FIG. 1, in a hybrid electric vehicle to which a
transmission mounted electric device (TMED) system is applied, an
engine clutch 3 is installed between an engine 2 and a motor 1 for
driving, and the engine clutch 3 is configured so as to transmit
power between the engine 2 and the motor 1. According to the
operation of the engine clutch 3, the engine 2 and the motor 1 are
physically connected and thus the power of the engine 2 may be
transmitted to driving wheels 9, or the engine 2 and the motor 1
are physically disconnected and thus the power of the engine 2 may
not be transmitted to the driving wheels 9.
The above hybrid electric vehicle may use a combination of the
power of the engine 2 and the power of the motor 1 while driving.
The hybrid electric vehicle drives using only the power of the
motor 1 in an electric vehicle (EV) mode, and drives using the
power of the motor 1 and the power of the engine 2 in a hybrid
electric vehicle (HEV) mode.
The conventional hybrid vehicle drives using only the power of the
motor 1 in an initial stage of launching of the vehicle during
parking, and then uses the power of the engine 2 according to a
driver request or the state of charge (SOC) of a battery 6. The
battery 6 is used as the power of the motor 1. The power of the
engine 2 may be transmitted to a drive shaft 8 and the driving
wheels 9 through the engine clutch 3 and a transmission 4, and
excess power out of the power of the engine may charge the battery
6 using the motor 1.
In order to transmit the power of an engine to wheels or to use the
power of the engine to charge a battery, an engine clutch should be
physically engaged. However, due to characteristics of the engine,
engagement of the engine clutch and power transmission using the
engine clutch are impossible at a low RPM (for example, 1000 RPM or
lower). The reason for this is that, when the engine clutch is
engaged at a low RPM of the engine, an unstable state of the
engine, such as a stall, occurs.
The maneuvers to control engagement of the engine clutch are
classified into two methods, i.e., synchronization engagement
control and launch slip engagement control. In other words, the
synchronization engagement control is referred to as
synchronization connection control, and the launch slip engagement
control is referred to as launch slip connection control.
In the synchronization engagement control, a real-time motor speed
is set to a target speed of the engine, an engine speed is
controlled by a hybrid starter generator (HSG) 5 (in FIG. 1) so as
to be synchronized with the motor speed, and then the engine clutch
is directly connected using hydraulic pressure. This
synchronization engagement control is used in conditions in which a
vehicle speed may be controlled using only the power of the motor.
Referring to FIGS. 2A to 2F, after a motor RPM and an engine RPM
are synchronized, an engine torque is gradually increased and a
motor torque is gradually decreased.
The launch engagement control is an engagement control method in
which an engine torque is transmitted to the wheels through slip
control of the engine clutch so as to raise a vehicle speed and a
motor RPM, and thereby, when the motor speed is synchronized with
the engine speed to a designated speed or less, the engine clutch
is directly connected. That is, the launch engagement control is
configured that the engine clutch is directly connected when the
motor speed is synchronized with the engine speed to the designated
speed or less during slip control of the engine clutch. Referring
to FIGS. 2A to 2F, before the motor RPM and the engine RPM are
synchronized, the engine torque is transmitted to the wheels
through slip control of the engine clutch and thus the motor RPM is
raised.
This launch slip engagement control is used if it is impossible to
raise the motor RPM to a designated RPM or more using only the
power of the motor. If it is impossible to raise the motor RPM to
the designated RPM or more using only the power of the motor, the
engine clutch may not be engaged and thus the power of the engine
may not be transmitted to the wheels. For example, if the SOC of
the battery is low, if the vehicle is in an extremely low
temperature environmental condition, or if the vehicle drives on a
steep slope, it is impossible to raise the motor RPM to the
designated RPM or more using only the power of the motor.
The engagement control method of the engine clutch may be
determined at the initial stage of launching of the vehicle based
on the state of vehicle, driving conditions, etc.
However, conventionally, when the engagement control method of the
engine clutch can be determined at the initial stage of launching
of the vehicle, and the synchronization engagement control is
preferentially attempted without considering the state of the
vehicle and driving conditions. Thereafter, time-out conditions
depending on the vehicle state and the driving conditions are
applied, and thus, when a designated time corresponding to the
time-out conditions elapses during execution of the synchronization
engagement control, the launch slip engagement control starts to be
executed. The reason for this is that a control factor to determine
the engine clutch engagement control method is not clear, and
conversion of the engine clutch engagement control method to the
launch slip engagement control during execution of the
synchronization engagement control is possible but conversion of
the engine clutch engagement control method to the synchronization
engagement control during execution of the launch slip engagement
control is not possible.
In the present disclosure, an engagement control method of an
engine clutch is determined based on specifications and state
information of a vehicle and driving and environment information,
and thus, accuracy to determine the engagement control method of
the engine clutch may be increased and a determination error of the
engagement control method and transition of the engagement control
method thereby may be minimized.
Engagement control of the engine clutch refers to a series of
controls which is performed to directly connect the engine clutch,
and direct engagement of the engine clutch means a state in which
the engine clutch is physically engaged and connected so that power
of an engine is transmittable to wheels. That is, direct connection
of the engine clutch may be attempted by executing the engagement
control of the engine clutch, and the engine clutch may be actually
directly connected when the engagement control of the engine clutch
is completed.
A method for controlling engagement of an engine clutch in
accordance with the present disclosure may be implemented by
controllers which are installed in advance in a vehicle. More
particularly, the method may be executed by an engine controller, a
motor controller, a transmission controller, a hybrid controller,
etc. The hybrid controller may be a higher-level controller of the
engine controller, the motor controller and the transmission
controller. The engine controller may control the overall operation
of an engine system in the vehicle including an engine, and the
motor controller may control the overall operation of a motor
system in the vehicle including a motor. The transmission
controller may control the overall operation of a transmission.
In the method in accordance with the present disclosure, if
engagement control of the engine clutch 3 is required, more
particularly, if conversion of a driving mode of the vehicle to the
HEV mode during driving in the EV mode, like at the initial stage
of launching of the vehicle, is required by a driver, the
synchronization engagement control may be executed or the launch
slip engagement control may be executed according to a result of
determination as to whether or not a condition for execution of the
synchronization engagement control is satisfied.
Referring to FIG. 3, the method in accordance with the present
disclosure includes determining whether or not driving of the
vehicle in the HEV mode is required during driving in the EV mode,
determining whether or not at least one of two or more conditions
for execution of synchronization engagement control of the engine
clutch 3 is satisfied when driving of the vehicle in the HEV mode
is required, executing the synchronization engagement control when
the at least one of the two or more conditions for execution of the
synchronization engagement control is satisfied, and executing
launch slip engagement control of the engine clutch 3 when all of
the two or more conditions for execution of the synchronization
engagement control are not satisfied.
In the determination as to whether or not driving of the vehicle in
the HEV mode is required during driving in the EV mode, whether or
not conversion of the driving mode of the vehicle to the HEV mode
is required may be determined based on a driver request torque.
When the driver request torque exceeds a maximum torque which the
motor 1 may output in real time during driving in the EV mode, it
may be determined that conversion of the driving mode of the
vehicle from the EV mode to the HEV mode is required.
The driver request torque may be detected by an accelerator
position sensor (APS) which detects the position of an accelerator
pedal (i.e., a movement amount of the accelerator pedal). The
driver request torque may be calculated using a torque map which is
constructed to determine the driver request torque according to the
position value of the accelerator pedal.
In the determination as to whether or not the at least one of the
two or more conditions for execution of the synchronization
engagement control is satisfied, whether or not the two or more
conditions for execution of the synchronization engagement control
of the engine clutch 3 are satisfied is determined based on a first
condition, a second condition, a third condition and a fourth
condition. When at least one of the first to fourth conditions is
satisfied, it may be determined that the vehicle is in a situation
in which the synchronization engagement control is executable. That
is, when the at least one of the first to fourth conditions is
satisfied, it may be determined that the condition for execution of
the synchronization engagement control of the engine clutch 3 is
satisfied.
The first condition is that a real-time revolutions per minute
(RPM) of the motor 1 is a first RPM or more. That is, when the
real-time RPM of the motor 1 is the first RPM or more, it may be
determined that the first condition is satisfied. The first RPM may
be set to a motor RPM value which ensures operation stability of
the engine 2 when the engine clutch 3 is engaged, in consideration
of characteristics of the engine 2. Specifically, the first RPM may
be set to a motor RPM value at which the motor 1 may transmit power
to the driving wheels 9 by tracking the torque of the engine 2 when
the engine clutch 3 is directly connected. Due to characteristics
of the engine 2, if the engine clutch 3 is directly connected at a
low RPM of the engine 2, the engine 2 becomes unstable and thus
accuracy in the torque of the engine 2 may be lowered. For example,
the RPM of the engine 2 which is less than 1000 RPM may be
determined as a state in which the RPM of the engine 2 is low. The
first RPM may be 1000 RPM or more. Referring to FIGS. 4A and 4B, a
motor RPM at a point in time when the driving mode of the vehicle
is converted to the HEV mode according to a driver request is the
first RPM or more, the synchronization engagement control may be
executed.
The second condition is that a maximum RPM N.sub.MAXTQ of the motor
1 which may maintain the maximum torque of the motor 1 based on the
real-time available power of the motor 1 is a second RPM (i.e., an
engine clutch direct connection RPM) or more. That is, when the
maximum RPM N.sub.MAXTQ of the motor 1 is the engine clutch direct
connection RPM or more, it may be determined that the second
condition is satisfied. The maximum torque of the motor 1 is a
motor torque which may be generated based on the real-time
available power of the motor 1. The real-time available power of
the motor 1 may be the real-time available power of the battery 6
which is used as the power of the motor 1. Since the motor 1
generates a torque using the power of the battery 6, the motor
torque is changed according to the power of the battery 6 which is
determined based on the SOC of the battery 6 and temperature, and
thus, the RPM which may ensure the maximum torque of the motor 1 is
also changed according to the power of the battery 6. Referring to
FIG. 5, the maximum torque TQ.sub.MAX of the motor 1 based on the
available power of the motor 1 is maintained to a designated RPM,
i.e., the maximum RPM N.sub.MAXTQ.
Further, the engine clutch direct connection RPM is an RPM at a
point in time when the power of the engine 2 starts to be
transmitted to the drive shaft 8 of the vehicle by direct
connection of the engine clutch 3 due to hydraulic pressure
supplied from a hydraulic pump 7 (in FIG. 1) after synchronization
between the RPM of the engine 2 and the RPM of the motor 1. That
is, the engine clutch direct connection RPM is the RPM of the
engine 2 and the motor 1 when the engine clutch 3 is directly
connected. For example, the engine clutch direct connection RPM may
be 1300 RPM or more.
In addition, a torque value of the motor 1 may be calculated using
Equation 1 below. TQ=P.sub.ELEC/(N.sub.motor.times.2.pi./60)
[Equation 1]
Here, TQ is motor torque, P.sub.ELEC is power of the battery 6, and
N.sub.motor is motor RPM.
The third condition is that a maximum RPM of the motor 1 which may
satisfy the driver request torque based on the real-time available
power of the motor 1 is the engine clutch direct connection RPM or
more. That is, when the maximum RPM of the motor 1 is the engine
clutch direct connection RPM or more, it may be determined that the
third condition is satisfied. The maximum RPM of the motor 1 which
may satisfy the driver request torque and the maximum RPM of the
motor 1 which may maintain the maximum torque of the motor 1 may
have different values (referring to FIGS. 5 and 6). Referring to
FIG. 6, the motor torque which may correspond to the driver request
torque is maintained only up to a designated RPM N.sub.DERATINGTQ.
Therefore, a maximum RPM of the motor 1 which may maintain a motor
torque, which is the driver request torque or more, is the RPM
N.sub.DERATINGTQ.
The fourth condition is that acceleration linearity of the vehicle
is satisfied. Whether or not acceleration linearity of the vehicle
is satisfied may be determined based on a result of comparison
between an excess acceleration and a threshold acceleration.
Specifically, when the excess acceleration is the threshold
acceleration or more, it may be determined that acceleration
linearity of the vehicle is satisfied. The excess acceleration may
be an acceleration which is actually generated during driving of
the vehicle, and the excess acceleration may be determined based on
the excess torque and weight of the vehicle. Furthermore, the
excess acceleration may be calculated as a value acquired by
dividing the excess torque of the vehicle by the weight of the
vehicle.
The excess torque is an excess driving force F.sub.NET of the
vehicle for actual driving. That is, the vehicle may drive using
the excess torque. Referring to FIG. 7, the excess torque F.sub.NET
may be determined as a value acquired by subtracting a driving load
of the vehicle from an available torque of the vehicle. The
available torque of the vehicle is an available torque of the
wheels (i.e., the drive wheels) 9, and the available torque of the
vehicle may be calculated as a value acquired by dividing a
real-time torque of the motor 1 by a gear ratio of the transmission
4 (in FIG. 1) and a dynamic radius of tires. The driving load is a
driving load applied to the driving wheels 9, and the driving load
may be determined based on specifications information and a driving
speed of the vehicle and a slope of a driving road. Specifically,
the driving load may be calculated based on a rolling resistance
.mu. of the tires, a weight m of the vehicle, driving system drag,
an aerodynamic force, and a slope .theta. of a driving road. The
driving system drag is drag generated by a driving system of the
vehicle during driving, and the driving system drag may be a drag
torque of the transmission 4. The drag torque may be a torque
generated by a transmission oil drag phenomenon. The driving load
may be calculated using Equation 2 below. Driving
Load=(.mu..times.m.times.g.times.sin .theta.)+(Drag Torque of
Transmission.times.V)+(1/2.times..rho..times.Cd.times.A.times.V.sup.2)
[Equation 2]
Here, g is acceleration due to gravity, V is a vehicle speed, .rho.
is air density, Cd is an air resistance coefficient of the vehicle,
and A is a cross-sectional area of the vehicle. The cross-sectional
area of the vehicle is a cross-sectional area of the vehicle which
encounters air resistance during driving.
The threshold acceleration may be an acceleration value which is
set in advance through tests. The threshold acceleration may be
changed according to the gear ratio of the transmission 4
connecting the motor 1 and the drive shaft 8. That is, the
threshold acceleration may be an acceleration value which is set
according to the gear ratio of the transmission 4. Specifically,
the threshold acceleration may be set to different values if the
gear position of the transmission 4 is the position D and if the
gear position of the transmission 4 is the position R.
On the other hand, when all of the first to fourth conditions are
not satisfied, the launch slip engagement control of the engine
clutch 3 is executed. Further, although at least one of the first
to fourth conditions is satisfied and thus the synchronization
engagement control is executed, when a reference time elapses
before direct connection of the engine clutch 3, the execution of
the synchronization engagement control is stopped and the launch
slip engagement control starts to be executed. That is, when the
reference times elapses while attempting direct connection of the
engine clutch 3 by the synchronization engagement control, the
launch slip engagement control is executed. In other words, when
physical engagement of the engine clutch 3 is not carried out until
the reference time elapses from start of the execution of the
synchronization engagement control, the launch slip engagement
control is executed. The reason for this is that, even if at least
one of the conditions for execution of the synchronization
engagement control is satisfied in terms of the driving force or
acceleration linearity of the vehicle, when the vehicle drives
using only the motor 1 for a designated time before direct
connection of the engine clutch 3 for the reference time, the power
of the battery 6 is consumed. In other words, the vehicle drives
using only the driving force of the motor 1 while direct connection
of the engine clutch 3 is attempted through the synchronization
engagement control, and, as a time taken to drive the vehicle using
only the driving force of the motor increases, the SOC of the
battery is reduced and thus SOC balancing of the battery 6 is
lowered. Such a phenomenon mainly occurs, for example, if the
vehicle drives on an uphill road or if the driving system drag is
high in winter. Therefore, when the reference time elapses, the
engagement control method of the engine clutch 3 is converted to
the launch slip engagement control, thus being capable of
preventing exhaustion of the SOC of the battery 6. When the
engagement control method of the engine clutch 3 is converted to
the launch slip engagement control, slip control of the engine
clutch 3 is performed, a portion of power of the engine 2 is
transmitted to the drive wheels 9, and thereby, the amount of power
of the motor 1 used may be reduced and SOC balancing of the battery
6 may be ensured. Here, the reference time may be determined
depending on the SOC of the battery 6, a slope of a driving road
and a gear position (gear ratio) of the transmission 4.
Specifically, as the SOC of the battery 6 increases, the reference
time may be lengthened, and as the SOC of the battery 6 decreases,
the reference time may be shortened. Further, as the slope of the
driving road increases, the reference time may be shortened, and as
the slope of the driving road decreases, the reference time may be
lengthened.
Referring to FIGS. 8A to 8C, if the launch engagement control is
executed, slip control of the engine clutch 3 is performed by
applying hydraulic pressure to the engine clutch 3 before
synchronization between the engine RPM and the motor RPM, and
thereby, a portion of power of the engine 2 is transmitted to the
drive wheels 9. The amount of power of the motor 1 used may be
reduced by the engine torque (i.e., driving force) transmitted to
the driving wheels 9 through the slip control of the engine clutch
3, and thereby, consumption of the SOC of the battery 6 may be
reduced.
Referring to FIG. 3, if the engagement control method of the engine
clutch 3 is converted to the launch slip engagement control
according to a driver request during driving in the EV mode, the
engagement control method of the engine clutch 3 may be determined
as follows.
First, whether or not conversion of the driving mode of the vehicle
from the EV mode to the HEV mode is required based on a driver
request torque is determined (S10). If conversion of the driving
mode of the vehicle from the EV mode to the HEV mode is required,
whether or not the real-time RPM of the motor is the first RPM or
more is determined (S12). When the motor RPM at a point in time
when the driving mode of the vehicle is converted from the EV mode
to the HEV mode is the first RPM or more, the synchronization
engagement control is executed (S14).
When the motor RPM at the point in time when the driving mode of
the vehicle is converted from the EV mode to the HEV is less than
the first RPM, whether or not a maximum RPM N.sub.MAXTQ of the
motor 1 which may maintain the maximum torque of the motor 1 based
on the real-time available power of the motor 1 is the engine
clutch direct connection RPM or more is determined (S16). When the
maximum RPM N.sub.MAXTQ of the motor 1 is the engine clutch direct
connection RPM or more, the synchronization engagement control is
executed (S18).
When the maximum RPM N.sub.MAXTQ of the motor 1 is less than the
engine clutch direct connection RPM, whether or not a maximum RPM
of the motor 1 which may satisfy the driver request torque based on
the real-time available power of the motor 1 is the engine clutch
direct connection RPM or more is determined (S20). When the maximum
RPM of the motor 1 is the engine clutch direct connection RPM or
more, the synchronization engagement control is executed (S22).
When the maximum RPM of the motor 1 is less than the engine clutch
direct connection RPM, whether or not acceleration linearity of the
vehicle is satisfied is determined (S24). When acceleration
linearity of the vehicle is satisfied, the synchronization
engagement control is executed (S26). When an excess acceleration
of the vehicle is a threshold acceleration or more, it may be
determined that acceleration linearity of the vehicle is satisfied.
When acceleration linearity of the vehicle is not satisfied, the
launch slip engagement control is executed (S28).
In operations S14, S18, S22 and S26, whether or not a reference
time T elapses after start of the execution of the synchronization
engagement control is determined (S30). When the reference time T
elapses after start of the execution of the synchronization
engagement control, the launch slip engagement control is executed
(S32). That is, when direct connection of the engine clutch 3 due
to the synchronization engagement control is not carried out within
the reference time T, the execution of the synchronization
engagement control is stopped and the launch slip engagement
control starts to be executed.
As is apparent from the above description, in a method for
controlling engagement of an engine clutch in a hybrid electric
vehicle in accordance with the present disclosure, a control factor
to determine an engagement control method of the engine clutch is
clearly constructed, and thus, the engagement control method of the
engine clutch at a point in time when engagement control of the
engine clutch is necessary may be accurately determined so as to
minimize a determination error of the engagement control method and
conversion of the engagement control method thereby.
That is, in the method in accordance with the present disclosure,
unnecessary conversion of the engagement control method due to a
determination error of the engagement control method may be
minimized, and a sense of discontinuity caused by conversion of the
engagement control method may be minimized.
The present disclosure has been described in detail with reference
to preferred embodiments thereof. However, it will be appreciated
by those skilled in the art that changes may be made in these
embodiments without departing from the principles and spirit of the
disclosure, the scope of which is defined in the appended claims
and their equivalents.
* * * * *